Issue link: https://iconnect007.uberflip.com/i/948150
50 SMT007 MAGAZINE I MARCH 2018 paste volume delivered by the thicker foil, the trend in fact is just the opposite with the thin- ner foil supplying more volume. Reasoning for this is the combination of a more challenging area ratio on the 80mm thick stencil that limits paste transfer efficiency along with the poor stencil wipe condition inside the 50mm thick step areas which boosts print volume. Further review of Figure 15 results show there are a few test conditions that nearly satisfy the mini- mum 0.48nl paste volume requirement. The data distributions can be dissected in more detail by exploring the raw print volume distri- butions on an individual print basis, which is explored in Figures 16, 17, and 18. While the format of the boxplots in Figures 16, 17, 18 are labeled for clear interpretation, two key performance metrics necessitate clarification. First, the 0.48nl paste volume thresh- old is drawn in these plots now as a blue colored dashed horizontal line. Second, the outline color of the indi- vidual boxplot is either red or black. Red boxplot outlines indicate the print volume distribution exceeds a volume transfer efficiency standard deviation value of 10%. Black boxplot outlines indicate the standard deviation is less than 10%. The objective for investi- gating these detailed boxplot views is to determine which data, if any, can satisfy both conditions (i.e., >0.48nl, <10% Std. Dev.). Figure 16 contains several occurrences of compliant data, representing the printing process test on bare Cu boards. The flatter board topography is considered a significant advantage towards achieving highly uniform prints. Despite the challenge of effi- cient squeegee wiping inside the 50mm thick step area, several boards were printed quite well. Fewer successes were reported with the thicker 80mm apertures, as expected with lower area ratio apertures. The print by print results in Figure 17 contains LG pad data. Some of the boards printed with nano-coated stencil apertures satisfy the 0.48nl paste volume requirement, however, none of Figure 15: Raw volume boxplot – all prints combined. Figure 16: Individual print boxplots – bare Cu pads. Figure 17: Individual print boxplots – large Cu pads.